I encountered some guys saying Christians are not allowed to use Musical Instriments in Worship. I never heard of such a dumb viewpoint.
Ah yes, we have a few of... Ahem... That particular church organization... In my area. They always seem to be ready for an argument, even deliberately seeking arguments. Their conversation is always loaded with bait to start argum... ah, "discussions" so they can loudly state their views. As if we missed their views the first 300 times.
Three things I will point out though:
1 - I can't see where doing without musical instruments does them any actual harm, so I just avoid talking to them when I can and decline to debate when I have to talk to them.
2 - As Paul once said, if you do something believing it is wrong - even if there's nothing really wrong with it - to you it is a sin, because you are deliberately doing something you think is wrong. So not only is there no profit in arguing with them, there can be actual harm.
3 - There was a real cool older guy I used to work with. I worked with him for YEARS before I happened to find out he was part of that church. It just never had come up before. And when it did come up, he wasn't all defensive and argumentative about it. I wound up giving him a few good acappella albums I had. Just keep in mind that every human is an individual. No matter how many people from that kind of church argue with you, there are still a few who are cool dudes.